Generally, some DC to AC conversion circuits may have an inverter, and most of the inverters generate pulse width modulation (PWM) signals by using a high frequency switching manner. This may cause a great amount of high frequency harmonic current which influences the next stage circuits or equipments and causes some problems in the next stage circuits or equipments. Therefore, a filter connected to the AC output terminal of the inverter is quite important for the element selection and circuit design of a DC to AC conversion circuit.
Under the condition of the same inductance, as comparing with conventional L type filters, a LCL type filter is ideal for suppressing high frequency harmonic, and is gradually applied to the inverter having a high power and a low switching frequency.
Compared with the first order L filter, the LCL filter can meet the grid interconnection standards with significantly smaller size and cost, especially for applications above several kilowatts, but it might be more difficult to keep the system stable.
Although the LCL type filter has a good performance of filtering high frequency harmonic, the design process thereof is complicated and requires a trail-and-error manner of obtaining proper parameters because the character of the LCL type filter is easily affected by these parameters. Therefore, it is necessary to improve such DC to AC conversion circuits.